Since the seventies, Messrs AIM AEG Infrarot Module GmbH has been manufacturing high-quality Infrared detectors and associated components such as heat sinks and read-out electronics. The detectors are used by the military, for research, in medicine and in industry. In the latest generation of detectors, the separate elements are arranged in a two-dimensional structure in the surface and a mechanical scanner is no longer required for image formation. With the two-dimensional detector, a suitable optical system can project a scene directly onto the photosensitive chip. The separate elements are read out sequentially and additional computer processing re-assembles them to a two-dimensional data structure, an image.
The technology causes detector inhomogeneity in the separate elements, thus producing an imaging error. There is both time-invariant and time-variant inhomogeneity. Previous line cameras, with a one-dimensional detector structure, solve the problem by having the detector look regularly at a reference source when scanning the scene and using this information to re-calibrate. The enormous expenditure involved in transferring this process to a detector with a two-dimensional structure makes it impractical. With two-dimensional detectors, time-invariant inhomogeneity can be corrected by a one-off calibration at a thermal reference source. It would then be possible to allow the user to post-calibrate time-variant inhomogeneity at a thermal reference source. This expenditure is worth avoiding.